Electronic documents that include Word, Power Point and Excel files generated by employees in an organization often contain sensitive information that should be made available to only a selected set of recipients with a security classification level that is appropriates for viewing the information contained in the document. A document or its parts are associated with a certain security classification level whereas each recipient belongs to a security classification domain that determines the security classification levels of the documents that the recipient is allowed to receive. Consider for example a Word file that has a security classification level of “CLASSIFIED”. It can thus be viewed only by persons in a security classification domain with a security classification level that is equal to higher then “CLASSIFIED”.
Protecting electronic documents and ensuring that only authorized persons are given access to sensitive information contained in the documents is critically important to the appropriate functioning of the organization. Controlling document access based on the security classification level of the document has a number of advantages that include the following.                It reduces disclosure of sensitive information to unauthorized persons;        It facilitates the enforcement of policies regulating document distribution for the organization;        It enables the use of security technology to prohibit the “leaking” of the document to a recipient that does not have the authorization to view the information contained in the document.        
While existing document management systems have various features developed over a number of years, the problem of classified documents leaking into another security classification domain that does not include (or permit) the security classification level assigned to the document still exists. Therefore, there is a need in the industry for developing an improved method and system for introducing trusted security labels in electronic documents.